Hardware freaks Unite (on this one)
Adrian Godwin
agodwin at acorn.co.uk
Thu Apr 18 23:40:38 AEST 1991
In article <100 at fbits.ttank.com> Mariusz at fbits.ttank.com (Mariusz Stanczak) writes:
>In article <6386 at acorn.co.uk>, agodwin at acorn.co.uk (Adrian Godwin) writes:
>> A number of companies sell daughter boards - some of them based on the
>> Motorola app. note - as an upgrade for the Commodore Amiga. It seems to
>
> Yes, so do others for the Mac... the question for me would be
> are those boards system specific, i.e. do they assume (and "solve")
> anything about the hardware/software quirks of the given system
> for which they are marketed?
They may assume things about the bus timing - the critical timings on one
system may differ from those on another, and these add-ons aren't going to be as
well specified as say, an emulator. One card I know of adds some memory at a
fixed address (though it might be possible to change it with a different PAL)
- however, it does it at an address that can't exist on a 24-bit-address
68000 so it can't possibly conflict. Control registers may - or may not -
be similar.
>> inside an A500, they may be useable on the 3b1. This would at least reduce
>> the problem to the software part [...]
>
> So, as above... what would be the pitfals(sp). If such a "card"
> wouldn't be hardware specific, and (correct me anybody) since most
As I understand it, mostly to the kernel. The higher 680x0 processors
have a different interrupt/exception stack frame to the 68000, and the
system needs also to recognise memory that isn't in it's normal addressing
range. A different mechanism is used to load the PSR.
Perhaps there are other differences too - it's only a drop-in replacement
for the Amiga because its OS knows about alternative processors.
Even so, some applications do things they shouldn't, and fall over. This
should be less of a problem on the 3b1, because Unix applications are much
better behaved than those for OSs without process protection - but don't
forget to fix the diagnostics as well as the real OS ! Or use an upgrade
card that makes it possible to switch between a 68020 and a real 68000.
--
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Adrian Godwin (agodwin at acorn.co.uk)
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